#include <iostream>
#include <algorithm>
#include <string>
#include <queue>
#include <vector>
#include <map>
#include <cstdio>
#include <cmath>
#define INF 100000000
using namespace std;

int main() {
	int n, sum = 0;
	cin >> n;
	for (int i = 1; i <= n; i++) {
		sum += i;
	}
	cout << sum << endl;
	return 0;
}